Abstract: A globally distributed system clock is received and selectively gated by local clock generators responsive to global control signals. The local clock generators, which are located proximately to sequential circuits having serial scan paths, produce scan and functional clock signals adapted to the sequential circuits, which may have a variety of required timing diagrams.

Abstract: A scannable LIFO register stack in which registers are arranged in a stack with each register having a number of bit locations. Each register is in communication with an adjacent register located above and below it. In particular, each bit location in a register within the stack located between the top and the bottom register is in communication with a corresponding bit location in an adjacent register located above the register and a corresponding bit location in an adjacent register located below the register. Except for the last bit, each bit location in the top register has a connection to an offset bit location in the bottom register. Shifting a bit of data from a bit location in the top register to the offset bit location in the bottom register results in the bit being shifted to the right by one bit location according to the present invention. The last bit location in the top register has an output that is used as a scan output.